Pickling bath for ferrous metals



Patented Aug. 27, 1946 PICKLING BATH FOB. FERROUS METALS Aaron D. Johnson, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 11, 1944, Serial No. 544,462

Claims. (Cl. 252150) This invention relates to metal pickling and more particularly to free-flowing pulverulent compositions in which a controlled proportion of a liquid thiazoline is dispersed on a finely divided solid of controlled particle size and to processes for preparing pickling baths for ferrous metals by adding such pulverulent compositions to aqueous solutions of non-oxidizing acids.

It is customary in metal pickling and cleaning processes to use a bath of a dilute non-oxidizing acid, such as sulfuric, hydrochloric, acetic, or formic acid, or an aqueous solution of an acid sulfate. Various iron or steel articles, such as wire, sheet, and other manufactures, are commonly pickled in such acids. The compositions, concentration, temperature of operation, and other factors may difier with the different baths, but in every instance the primary function of the bath is to remove undesirable incrustations. As soon as the base metal becomes exposed it is subject to attack by the acid with consequent damage to the article and with an unnecessary consumption of acid.

It has become the practice to control the action of acids on metals by adding to pickling baths small amounts of organic substances known as inhibitors. Such agents act to permit the acid to dissolve scale, such as iron oxide, but to letardmriprevent dissolution of the underlying basemetal. The class of compounds known as thiazolines, and especially thiazolinyl sulfides have recently been found to be excellent inhibitors.

Unfortunately thiazolines are liquids which dissolve slowly and sparingly in acid pickling baths. If given sumcient time they will dissolve in acids to a concentration ample to control the action of the acids on metals. In commercial pickling practice a bath is used as soon as it is made up and a sparingly or slowly soluble liquid inhibitor may not have time to dissolve and instead may float out as an oily layer on the surface, where it is picked up on the first work passing through, necessitating cleaning of the pickled work and wastefully reducing the concentration of inhibitor in the pickle. 'I'hese difficulties have led to a considerable prejudice against slowly soluble liquid inhibitors and a preference for rapidly soluble solid inhibitors.

Considerable advantages are derived by having an inhibitor in the form of a free-flowing pulverulent solid. Such products are easily handled, may be stored and shipped in a variety of containers, are easily measured out for addition to a pickling bath, either by weight or by volume,

and in general are in a form easier to use in commercial practice.

It is important, however, that the concentration of active ingredients in the pulverulent solid be relatively high since otherwise an unduly large bulk of inhibitor must be used to get the desired effect. Free-flowing. pulverulent solid inhibitors containing only a few percent of active liquid constituents may be easily produced using almost any comminuted carrier, but it is found that when the concentration of liquid in such mixtures exceeds say about 10% the mixture is no longer free-flowing but is a gummy or mushy mass.

Now it has been found in accordance with the present invention that if a liquid thiazoline is dispersed upon a finely divided solid having an average particle size of less than about 5 microns a free-flowing pulverulent composition is produced which may contain from 15 to by weight of liquid thiazoline and which is excellently adapted to be added to an aqueous solution of a non-oxidizing acid as a step in the preparation of a metal pickling bath. In a preferred g5 embodiment of the invention the finely solid carrier may be a calcium carbonate which reacts with the acid in the bath and evolves carbon dioxide, this gas evolution assisting in dispersing the thiazoline and minimizing the amount of agi- 30 tation required.

Through the medium of the present invention all of the advantages of a solid inhibitor above described are imparted to liquid thiazolines. Moreover, in the compositions of this invention the concentration of active ingredient is surficiently large that no undue bulk of the compositions is required to give the desired effect in metal pickling baths.

In the compositions of this invention the finely divided solid serves as a carrier for the liquid thiazoline. The average particle size of the carrier should be less than about five microns. This average particle size may be determined by any of the methods well known in the art such as microscopic examination, sedimentation, or any of the various means for gravitational classification. Uniformity of particle size is desirable; that is, all of the particles should be finely divided, although all do not need to be less than five microns in size so long as the average size is within the indicated range. It is preferred that all of the particles be less than about 200 microns so that all of the solid would pass through a standard mesh screen or sieve.

The finel divided solid preferably should be dilute aq eous acid bath in the concentration in which it would be added with the amount of thiazoline required to give the desired inhibition. For instance, if a concentration of 0.025% by weight of a thiazoline: is desired in the bath and a composition containing 20% by weight of thiazoline and 80% of carrier is to be used, the carrier preferably should be soluble in the bath to the extent of 0.1% by weight. Such materials as common salt, calcium sulfate, and calcium carbonate are cheap and are easily produced in the desired state of subdivision and hence represent preferred materials for use as carriers in the compositions of this invention, although other materials such as sodium sulfate, sodium carbonate, clays, bauxite, talc, and similar materials may be employed.

Particularly preferred carriers are calcium sulfate and calcium carbonate. Although these agents are commonl thought of as insoluble in sulfate solutions it is to be remembered that in the concentrations used they would be soluble in the pickling bath. Th calcium carbonate of course reacts with the acid of the pickling bath to evolve gaseous carbon dioxide and form the calcium salt of the anion of the acid in the bath. This gas evolution provides a degree of agitation of the inhibitor in the bath and facilitates dispersion and dissolution of the thiazoline.

Any liquid thiazoline may be used advantageously in the compositions of this invention. As here used, the term thiazoline is a generic designation including both the simple thiazolines and also thiazolinyl sulfides, Representative of the thiazolines which may be used are the following:

2-mercaptothiazoline 2-dodecylamin 5-methyl thiazoline n-Amyl 2-thiazolinyl sulfide Beta-hydroxyethyl 2-thiazolinyl sulfide 1,2 -ethylene di(2-thiazolinyl sulfide) Benzyl 2-thiazolinyl sulfide Beta-naphthylarninomethyl 2-thiazolinyl sulfide Beta-phenoxyethyl 2-thiazolinyl sulfide n-Butyl 2-thiazolinyl sulfide Beta-hydroxypentyl 2-thiazoliny1 sulfide Lauryl 2-thiazolinyl sulfide 2-methylthiazoline 2-phenylthiazoline Of the foregoing, it is particularly preferred to employ the beta-hydroxyethyl z-thiazolinyl sulfide.

The composition of the present invention may contain from about 15 to 35% by weight of liquid thiazoline, the balance to 100% being the finely divided solid. It will be understood, of course, that other ingredients may be present and if this is the case the proportions may be adjusted accordingly. That is, for 35 parts by weight of thiazoline there should be at least 65 parts of solid carrier and if an additional liquid is present the proportion of solid carrier should be correspondingly increased.

The method of mixing carrier must be such a material soluble in a the thiazoline with the as will effect dispersion of the liquid on the solid. Ideally the dispersion should provide a film of the thiazoline on each separate particle of the carrier. However, a lesser degree of dispersion will sumce provided the dispersion is sufficient to give a substantially uniform product. Uniformity may readily be judged by observing the free-flowing character of the product; that is, if the product is free-flowing the degree of dispersion is generally satisfactory,

Effective mixing may be obtained b such methods as spraying the liquid thiazoline upon the carrier, preferably while the carrier is agitated as by means of a ribbon blender. Alternatively, the liquid may be injected into the carrier while the carrier is being agitatedin a tumble barrel or tumble mill. Other similar devices for achieving the desired result will be readily apparent to those skilled in the art.

To make a pickling bath according to this invention one needs only to add to the pickling acid the desired quantit of pulverulent free-flowing thiazoline composition. Added in this way, the thiazoline readily goes into solution to give a bath ready for immediate use.

Th invention will be better understood by reference to the following illustrative examples.

Example I A pulverulent free-flowing product was made up b slowly adding 30 parts by weight of beta hydroxyethyl 2-thiazolinyl sulfide to '10 parts by weight of calcium carbonate having an average particle size of about two microns while the calcium carbonate was being agitated in a ribbon blender. The product thus obtained was added to an aqueous 10% sulfuric acid solution at a concentration of 0.083% by weight and was found to disperse readily and completely, The resultant solution was used for descaling steel and was found to be highly inhibited, that is, the acid readily removed the scale but did not attack the scale-free metal.

Example II A free-flowing pulverulent product was made by spraying 20 parts by weight of beta-hydroxyethyl 2-thiazolinyl sulfide onto parts by weight of calcium carbonate having an average particle size of about two microns while the calcium carbonate was being agitated in a tumble barrel. The resultant product was found to disperse readily and completely when added to a 10% sulfuric acid solution at a concentration of .125% by weight.

Example III A free-flowing pulverulent product was made by mixing 20 parts by weight of beta-hydroxyethyl 2-thiazolinyl sulfide with 80 parts by weight of hydrated calcium sulfate having an average particle size of about from four to five microns while the calcium'sulfate was being agitated in an edge runner mill. The resultant mixture was found to disperse readily in an aqueous 5% sulfuric acid solution.

While in the foregoing description of this invention certain specific compositions and processes have been set forth in detail, it will be understood that these are illustrative only and that one skilled in the art without departing from the scope of the invention may produce related products and employ related processes.

I claim:

1. A free-flowin pulverulent composition adapted to be dispersed in an aqueous acid solution to form a metal-pickling bath, the composition comprising about from fifteen to thirty five per cent by weight of a liquid thiazolinyl sulfide dispersed on a finely divided solid soluble in a dilute aqueous acid bath in the concentration in which it would be added with the amount of thiazolinyl sulfide required to give the desired inhibition and having an average particle size of less than about five microns and a maximum particle size of less than about 200 microns.

2. A free-flowing, pulverulent composition adapted to be dispersed in an aqueous acid solution to forma metal-pickling bath, the composition comprising about from fifteen to thirty five per cent by weight of beta hydroxyethyl 2- thiazolinyl sulfide dispersed on a finely divided solid soluble in a dilute aqueous acid bath in the concentration in which it would be added with the amount of thiazolinyl sulfide required to give the desired inhibition and having an average particle size of less than about five microns and a maximum particle size of less than about 200 microns.

3. A free-flowing, pulverulent composition adapted to be dispersed in an aqueous acid solution to form a metal-pickling bath, the composition comprising about from fifteen to thirty five per cent by weight of beta hydroxyethyl 2- thiazolinyl sulfide dispersed on a finely divided calcium sulfate having an average particle size of less than about five microns and a maximum particle size of less than about 200 microns.

4. A free-flowing, pulverulent composition adapted to be dispersed in an aqueous acid solution to form a metal-pickling bath, the composition comprising about from fifteen to thirty five per cent by weight of beta hydroxyethyl 2- thiazolinyl sulfide dispersed on a finely divided calcium carbonate having an average particle size of less than about five microns and a maximum particle size of less than about 200 microns.

5. A free-flowing, pulverulent composition adapted to be dispersed in an aqueous acid solution to form a metal-pickling bath, the composition comprising about thirty per cent by weight of beta hydroxyethyl 2-thiazolinyl sulfide dispersed on a finely divided calcium carbonate having an average particle size of less than about five microns and a maximum particle size of less than about 200 microns.

6. In a process for preparing a pickling bath for ferrous metals the step comprising adding to an aqueous solution of a non-oxidizing acid a composition comprising about from fifteen to We .thirtgfivelpenrcent by weight ot a liquid thiazolinyl sulfide dispersed on a finely divided solid 'solubledn adiluteaqueousacld bath in the con- 6 centration in which it would be added with the amount of thiazolinyl sulfide required to give the desired inhibition and having an average particle size of less than about five microns and a maximum particle size of less than about 200 microns.

7. In a process for preparing a pickling bath for ferrous metals the step comprising adding to an aqueous solution of a non-oxidizing acid a composition comprising about from fifteen to thirty five per cent by weight of beta hydroxyethyl 2-thiazolinyl sulfide dispersed on a finely divided solid soluble in a dilute aqueous acid bath in the concentration in which it would be added with the amount of thiazolinyl sulfide required to give the desired inhibition and having an average particle size of less than about five microns and a maximum particle size of less than about 200 microns.

8. In a process for preparing a pickling bath for ferrous metals the step comprising adding to an aqueous solution of a non-oxidizing acid a composition comprising about from fifteen to thirty five per cent by weight of beta hydroxyethyl 2-thiazoliny1 sulfide dispersed on a finely divided calcium sulfate having an average particle size of less than about five microns and a maximum particle size of less than about 200 microns.

9. In a process for preparing a pickling bath for ferrous metals the step comprising adding to an aqueous solution of a non-oxidizing acid a composition comprising about from fifteen to thirty five per cent byweight of beta hydroxyethyl 2-thiazolinyl sulfide dispersed on a finely divided calcium carbonate having an average particle size of less than about five microns and a maximum particle size of less than about 200 microns.

10. In a process for preparing a pickling bath for ferrous metals the step comprising adding to an aqueous solution of a non-oxidizing acid a composition comprising about thirty per cent by weight of beta hydroxyethyl 2-thiazo1iny1 sulfide dispersed on a finely divided calcium carbonate having an average particle size of less than about five microns and a maximum particle size of less than 200 microns.

AARON D. JOHNSON. 

